1. Field of the Invention
The present invention relates to a method and an apparatus for measuring a quality of a reverse link and the traffic load applying to a base station (BTS) in a CDMA mobile telecommunication system.
2. Description of the Related Art
In a CDMA mobile telecommunication system, a lot of mobile stations (MSs) communicate with each other via a single frequency allocation (FA). For this reason, the interference from other users has an effect on the quality of communication and the capacity of a system. While the interference of other users does not matter in a forward link since forward signals of all users are synchronous with orthogonal Walsh codes allocated respectively, the interference added to a reverse link has a great effect on the practical performance and capacity of a reverse link since each signal is asynchronous and used codes are not orthogonal each other.
The quality and the performance of a reverse link is highly dependent on the situation of a BTS, the environmental factors for MSs such as the number and moving velocity of a connected MS, moving status, and the quantity of packets being sent, the precision of power control, and the characteristics of air channels providing the signal paths between MSs and a BTS.
To measure the quality of a reverse link, a conventional method would include the step of measuring the quality of a forward link. This is accomplished by using a RSSI (Received Signal Strength Indicator) or Ec/Io (Pilot Power/Total received power), which is measured in a MS, a transmitting power (TX power) of a MS, or a transmission adjusting value of a MS to analyze the quality of a reverse link indirectly.
To measure the quality of a reverse link directly, a voice quality measuring device, for example CECAMS is used.
However, there is no way to measure the service quality such as call drop and bad access since the direct-measuring method can tell only the voice quality. This method can measure the quality of a reverse link of specific time and area when and where the measuring device is installed. These measurements must be made frequently because buildings surrounding a BTS change the wave propagation conditions. However, it is very difficult and uneconomic to examine the thousands of BTS environments by the direct-measuring device at any time. Moreover, the interference from the surrounding cells and the other users, which has a great effect on a reverse link, is not considered in the conventional method.
For this reason, there is an increasing need to measure the quality of a reverse link not temporarily but permanently without involving an operator in measuring the link quality.
To satisfy the need that the link quality between a MSs and a BTS should be automatically measured, the inventions of U.S. Pat. No. 5,623,484, U.S. Pat. No. 5,737,359, and Published Japan Application No. 96-65229 are presented.
However, these methods measure the quality of a reverse link by estimating the traffic based upon the instantaneous power level of the received signals from MSs. Therefore, one of the drawbacks is that the estimated traffic varies in accordance with the power level of received signals.
In practical mobile telecommunication systems, since numerous environmental factors change the power of received signals, and the estimated traffic, which was obtained from the proposed method, varies in a moment, the estimated traffic can not tell the practical traffic of a concerned BTS.
It is a primary object of the present invention to provide a method and an apparatus that can measure an accurate traffic load and a reverse-link quality of a mobile telecommunication system by statistically calculating the quality of a reverse link and the traffic load of a concerned BTS.
The method and apparatus for measuring the quality of a reverse link according to the present invention which will detect the received power of a BTS, convert the detected power into digital signal by sampling, calculate a ratio of the received power to the background noise power, construct the probability density function (PDF) and/or the cumulative distribution function (CDF) for the calculated ratio values, compare the constructed function with a chosen PDF and/or CDF of a theoretical ratio of a received power to a background noise power which is pre-calculated depending upon specified parameters, and determine the traffic load and the link quality based upon the comparison results.